The present invention relates to a process for producing flat-screen grids coated with non-evaporable getter materials and to the grids thereby obtained.
Intense interest has been directed to flat screens for several years as a replacement to conventional-sized bulky television-kinescopes and computer-screens. Among the various suggested types of flat screens, the so-called field emission displays (FEDs) seem to be particularly promising. Generally, a FED involves welding two flat glass members along their perimeter. The welding is carried out by melting a low-melting glass paste with an operation called "frit-sealing". The resulting structure is formed of two mutually parallel surfaces at a distance ranging from a few tenths of millimeters to 2-3 millimeters, thus defining an internal space. A plurality of sharpened microcathodes, made of metallic material, e.g. molybdenum, are provided on the inner surface, of the rear part, except along the edges. A plurality of grid electrodes are placed in close proximity to the microcathodes so that applying a small potential difference can produce a high voltage electric field that can extract electrons from the microcathodes. The electronic current is accelerated towards the phosphors placed on the inner surface of the front part, except for the edges. The zone containing the phosphors, corresponding and opposite to the zone having the microcathodes, is the image formation zone. The screen image is formed by selectively exciting only some phosphors.
In FEDs, the microcathodes and the phosphors are a few tenths of millimeters apart. The phosphors are selectively excited simply by selectively activating groups of microcathodes since the electronic beam is sufficiently collimated at these distances. However, one or more electric grids are needed to accurately direct the electronic beam to selectively excite phosphors in FEDs with an internal space that is 2-3 millimeters thick. These grids are generally formed of metal sheets that have a thickness ranging from 20 to 200 .mu.m and have the same surface area as the screen. The grids have a plurality of pinholes of size ranging from about 30 to 200 .mu.m and are spaced about 30-300 .mu.m apart.
The internal space of the FED must be kept evacuated to avoid dispersing the electronic beam. The residual pressures are usually more than 10.sup.-3 mbar for hydrogen, and not more than 10.sup.-4, and preferably less than 10.sup.-6 mbar, for other gases. Gases of various types may be emitted by the same FED composing materials during operation. As disclosed in patent applications WO 95/23425 and WO 96/01492, assigned to the Assignee of this application, herein incorporated by reference, maintaining the necessary vacuum inside the FEDs involves using non-evaporable getter materials, also known as NEG, that can fix gases such as O.sub.2, H.sub.2 O, CO, CO.sub.2 and N.sub.2.
At present, the NEG devices are disposed inside the FEDs in form of little pills or thin layers on the edges of the zone having the cathodes. This operation of the devices, however, transfers gas only slowly from the middle zone of the screen to the edges. This slow gas transfer can be a problem, particularly for large-sized FEDs, due to the thinness of the evacuated space of the FEDs space. Harmful gas concentration gradients can form inside the FEDs and hinder its proper operation.
It is an object of the present invention to deposit getter material so that it is spread out regularly on the entire screen surface.
This object is achieved according to the present invention, which in its first aspect relates to a process for the production of flat-screens grids coated with getter materials. The process involves providing a metal sheet being as thick as the resulting grid and having a surface area large at least as the image formation zone. The sheet is coated with one or more non-evaporable getter materials at least one side of the metal sheet. Portions of the metal sheet that are coated with getter material are then selectively removed.
All of these objectives, features and advantages of the present invention, and more, are illustrated below in the drawings and detailed description that follows.